Shock-absorbing intervertebral implant

ABSTRACT

The invention relates to an intervertebral implant comprising a spacer designed to be applied between two spinous processes of two vertebrae. The spacer comprises: two elements ( 10, 12 ) made of a first material, and each presenting a first end ( 10   a,    12   a ) and a second end ( 10   b,    12   b ), said first end ( 10   a,    12   a ) being securable to a spinous process; and a connection piece ( 14 ) made of a second material of greater elastic deformability than said first material, said connection piece interconnecting said second ends ( 10   b,    12   b ) of said two elements ( 10, 12 ) so that the stresses that are exerted on said two elements ( 10, 12 ) are damped, and said connection piece enabling said intervertebral implant to limit and brake the relative movements of said vertebrae.

This Application is a continuation of U.S. application Ser. No.11/800,676, filed May 7, 2007 , which is a continuation of U.S.application Ser. No. 10/332,412 filed on Jan. 7, 2003, issued as U.S.Pat. No. 7,238,204, which is a National Stage of PCT/FR01/02261 filedJul. 12, 2001, which claims priority to French patent 00 09093 filed onJul. 12, 2000, which are all incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an intervertebral implant designed tobe applied, in particular, between two spinous processes of twovertebrae.

BACKGROUND OF THE INVENTION

The indications for which this type of implant is inserted and fixedbetween the spinous processes generally originate from deterioration ofthe intervertebral disk. In particular, when the posterior portion of anintervertebral disk has deteriorated, extension of the spine causes thetwo vertebrae that are separated by the disk to move towards each otherabnormally. This generally causes the nerve roots to become trapped andcauses the person who is affected by this problem to experience pain.

Intervertebral implants comprising a spacer that is inserted between thespinous processes and that includes fixing means are well known. Thesespacers, generally made of titanium alloy, present a notch at each oftheir ends, with the spinous processes being received in the notches. Inaddition, the spacer is held by ties, interconnecting the two oppositeedges of each of the notches and tightened around part of the wall ofeach spinous processes.

Such implants limit the extent to which the vertebrae can move towardseach other since, when the spine is in extension, the spinous processestend to come into abutment against the bottoms of the opposite notchesin which they are inserted. However, the material of which the spacer ismade is hard compared with the material of an intervertebral disk which,when it is intact, limits the extent to which the vertebrae can movetowards each other, so much so that the jolts which can be transmittedto the spine, e.g. while walking, are not damped between two vertebraeinterconnected by a spacer. Furthermore, since the spacer does not havethe same mechanical properties as the remaining portion of theintervertebral disk, the overall mechanical properties of the spinepresent significant discontinuities compared with an intact spine,thereby increasing deterioration of the intervertebral disk.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an intervertebralimplant having two opposite notches against which the spinous processescome into abutment, which notches present relative mobility withrelative movements between them being damped.

To achieve this object the invention provides an intervertebral implantcomprising a spacer designed to be applied between two spinous processesof two vertebrae, the implant being characterized in that said spacercomprises:

two elements made of a first material, and each presenting a first endand a second end, said first end being securable to a spinous process;and

a connection piece made of a second material of greater elasticdeformability than said first material, said connection pieceinterconnecting said second ends of said two elements so that thestresses that are exerted on said two elements are damped, and saidconnection piece enabling said intervertebral implant to limit and brakethe relative movements of said vertebrae.

Thus, the connection piece situated between the two elements, eachsecured to a spinous process, tends to become compressed when thespinous processes move towards each other, and absorb the stressesexerted on said two elements. As a result, the vertebrae move towardseach other with a certain amount of elasticity that is close to thenatural elasticity conferred by an intact intervertebral disk.Furthermore, the relative elastic mobility of the vertebrae iscompatible with the elastic deformation of the posterior ligaments whichhold the vertebrae together. A system is thus obtained in which, understress, the relative mobility of its component elements is substantiallyidentical to the relative mobility of the elements of the originalintact system, thereby protecting the elements from furtherdeterioration.

In advantageous manner, said second ends of the spacer present asecuring wall onto which said connection piece is suitable for beingbonded. Thus, no additional fixing member is necessary and the adhesiveproperties of the second material co-operate with the securing wall.

In a particular embodiment of the invention, said securing wall presentsrecesses that are suitable for cooperating with projections of saidconnection piece in such a manner as to increase bonding between saidconnection piece and said wall. It will be understood that becauserecesses are formed in a wall, the surface area of said wall isincreased, thereby increasing the area of contact between the twomaterials when one of the materials can be molded onto the wall of theother. The increase in contact area increases the connection forcesbetween said connection piece and said two elements. Furthermore,recesses are formed in such a manner as to increase contact area andalso to increase the static friction forces between said two elementsand the material of the connection piece, said forces being in additionto the connection forces.

Advantageously, said second material of said connection piece isconstituted by a body obtained by polymerization. As a result, theconnection piece can easily be hot molded onto said elements if thematerial is polymerized beforehand, or it can be constituted in situ ifthe monomers constituting said second material polymerize at a speedthat is slow enough to provide enough time to make the assembly.

In a preferred embodiment of the invention, said first material of saidelements is a titanium alloy. It is thus easy to form recesses in saidsecuring wall onto which said connection piece is suitable for beingbonded.

In a first particular embodiment, each first end of said two elementsforms a notch between two wings that is suitable for receiving a spinousprocess, and said implant further comprises a tie of adjustable lengthinterconnecting said two wings, said tie surrounding a portion of saidspinous process in such a manner as to secure said first end to saidspinous process.

This characteristic of the intervertebral implant thus resides in theway said elements are fixed onto the spinous processes. A tie ispreinstalled on each of said elements of said spacer, and once saidspacer is inserted between two processes, said elements are secured tothe processes by tightening said ties.

In a second particular embodiment of the invention, each first end ofsaid two elements forms a notch between two wings that is suitable forreceiving a spinous process, and said implant further comprises a pinthat is suitable for passing laterally through said wings and saidprocess in such a manner as to secure said first end to said spinousprocess.

In this configuration, the spinous processes are pierced transversely,and the elements are connected thereto by means of a pin or rivet whichpasses both through the two wings of the element and through the processsituated between them. The pin or rivet is fixed onto one or both of thewings in such a manner as to prevent it from being removed accidentally.

In a third particular embodiment of the invention, each first end formsa notch between two wings that is suitable for receiving a spinousprocess, and said implant further comprises a clip-forming semicircularpart interconnecting said wings, said clip surrounding a portion of saidspinous process in such a manner as to secure said first end to saidspinous process.

As a result, the clips are easily fixed onto the wings of said elementsonce the spacer has been inserted. As explained in greater detail below,in this particular embodiment, since the wings are disengaged, thespacer is inserted without major surgery on the posterior ligaments.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear on readingthe following description of particular embodiments of the inventiongiven by way of non-limiting indication with reference to theaccompanying drawings, in which:

FIG. 1 is an axial section view of an intervertebral spacer of theinvention;

FIG. 2 is a diagrammatic view in elevation showing the intervertebralimplant provided with its adjustable fixing ties;

FIG. 3 is a diagrammatic view in elevation showing the intervertebralimplant provided with fixing pins; and

FIG. 4 is a diagrammatic view in elevation showing the intervertebralimplant provided with fixing clips.

FIGS. 5 and 6 are diagrammatic views showing other embodiments of theintervertebral spacer of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The spacer and the method of connecting the elements that constitute itare described initially with reference to FIG. 1.

The intervertebral implant includes two symmetrical elements 10 and 12each presenting a first end 10 a and 12 a and a second end 10 b and 12b. The two elements 10 and 12 are made of a bio-compatible material ofthe titanium-alloy type, suitable for remaining permanently inside thebody on the spine.

Each first end 10 a, 12 a presents a notch 10′a, 12′a in which a spinousprocess is capable of bearing in such a manner that each first end 10 a,12 a surrounds substantially half of the circumference of a process,said process passing through the first end 10 a, 12 a.

The elements 10 and 12 are interconnected by a connection piece 14,interposed between them, in such a manner that said elements 10 and 12are held symmetrically relative to each other. More precisely, it is thetwo ends 10 b and 12 b of the elements 10 and 12 that areinterconnected.

The connection piece 14 is constituted by a body, obtained bypolymerization, of the plastics-material type. The body is selected frommaterials having elastic deformability that is greater than that of thematerial of said elements 10 and 12, and especially having elasticproperties that are similar to those of the posterior ligaments whichhold the various elements of the spine together.

Organic silicon compounds form polymers having mechanical propertiesthat are capable of being determined by choosing their basicingredients, in elastic behavior that is preponderant compared withtheir plastic behavior. Thus, they constitute a family of materialssuitable for interconnecting said two elements 10 and 12. Furthermore,these polymers are capable of being highly adhesive on materials ofinorganic composition. Thus, when the elements 10 and 12 are made oftitanium alloy, the connection piece 14 provides a good connection.

However, suitable polymer-type materials are not restricted to theorganic silicon compounds and any other material presenting similarproperties could be used.

The material of said connection piece 14 is suitable for bonding onto asecuring wall of each of said two substantially plane ends 10 b and 12b. However, in order to increase adhesion, recesses 16 are formed in thesecuring walls of the ends 10 b and 12 b and these recesses are suitablefor co-operating with projections 18 of the connection piece 14 whichare inserted in the recesses 16.

This characteristic serves, firstly to increase the contact area betweenthe two materials, thereby increasing the connection force between themin a direction that is normal to said contact surface, and secondly tocreate static friction forces which are in addition to the bondingforce.

Such a connection is made either by injecting the hot polymer betweenthe two elements 10 and 12 held facing each other in a mold, or bymolding a cold mixture of monomers between the two elements 10 and 12 iftheir reaction speed is sufficiently slow. The projections 18 are thusformed in situ when the liquid or semi-liquid polymer inserted in therecesses 18 solidifies after cooling or after chemical reaction. It willbe understood that the connection piece 14 is constituted by the polymerinterposed between the elements 10 and 12, and that in order to maintainit between the facing elements while it is in the liquid state, thewalls of the mold must necessarily surround the space between the twoelements 10 and 12 in line with them.

In a particular embodiment, shown in FIG. 5, the recesses 16 formed inthe securing wall open out into the outside wall of the elements 10 and12 so that the liquid polymer penetrates completely into the recesses 16without any air being trapped therein. As a result, the connectionbetween the material of the connection piece 14 and the elements isstrengthened.

In addition, the recesses, shown parallel to the longitudinal axis ofthe spacer in FIG. 1, are capable of being formed obliquely relative tothe longitudinal axis and/or of being non rectilinear. Theseconfigurations enable the static friction forces of the polymer on theelements 10 and 12 to be increased, thereby strengthening theirinterconnection.

In another embodiment of the invention, shown in FIG. 6, the elements 10and 12 are axially pierced in the securing walls of their second ends 10b and 12 b in order to form a single recess opening out into their firstends 10 a and 12 a at the bottoms of their notches 10′a and 12′a. Aportion 14 a of the recess-forming hole situated in the vicinity of thenotch presents a diameter that is greater than that of the hole whichopens out into the securing wall, in such a manner as to form a shoulder50. The connection piece is thus molded between the elements 10 and 12in such a manner that the polymer-type material penetrates into the tworecesses and fills them completely as far as the bottom surfaces oftheir notches 10′a and 12′a. Furthermore, the diameter of the holes isgreater than the diameter of the recesses shown in FIG. 1. Thus, oncethe material of the polymer type has set, it not only secures the twoelements 10 and 12 by means of its adhesive properties on the insidewalls of the holes, but it also secures them mechanically since theportions of material molded in said greater-diameter portions come intoabutment against said shoulders.

Particular embodiments of the invention are described below withreference to FIGS. 2, 3, and 4.

FIG. 2 shows a first particular embodiment of the invention in which thetwo opposite edges of the notches 10′a and 12′a form wings 20, 21, 22,23 interconnected in pairs by ties 30 and 32 each having a portionbetween said wings 20, 21, and 22, 23 of a length that is adjustable,and each being locked by the tension which can be applied on said ties30 and 32.

FIG. 2 shows the two elements 10 and 12 connected by the connectionpiece 14. The implant of the invention is inserted between two spinousprocesses 34, 36 of two adjacent vertebrae in such a manner that the twonotches 10′a and 12′a, facing in opposite directions, respectivelyengage part of the adjacent bottom portion of the upper spinousprocesses 34 and part of the adjacent top portion of the lower spinousprocesses 36.

The ties 30 and 32 respectively pass round the top portion of the upperspinous process 34 and the bottom portion of the lower spinous process36 in such a manner that the spinous processes 34 and 36 are capable ofbeing locked in the respective notches 10′a and 12′a. Locking isperformed by tightening the ties 30 and 32, which, by means of slotsmade in the wings 21 and 23, are trapped in said wings 21 and 23.

Thus, the elements 10 and 12 are secured to the respective processes 34and 36, and relative movement of said processes 34, 36 is possiblewithin the deformation limits of the connection piece 14 made ofpolymer-type material.

When the two spinous processes 34 and 36 move towards each other, inparticular during extension of the spine, the two elements 10 and 12compress the connection piece 14 in elastic manner, i.e. the reactionforce which tends to hold the spinous processes 34 and 36 apart fromeach other is substantially proportional to the relative displacement ofthe two processes. Thus, the implant can take over the role of theintervertebral disk to be replaced (or the portion of the intervertebraldisk to be 5 replaced) concerning the spacing that it serves to maintainbetween two vertebrae so as not to trap any roots. It also makes itpossible for resulting is stresses which are applied to the spinousprocesses to be compatible with the stresses exerted on the processes bythe posterior ligaments.

Furthermore, when the two spinous processes 34 and 36 move away fromeach other, when bending the spine, the connection piece is subjected totraction having a return force that is also substantially proportionalto the elongation to which it has been subjected, at least for smallamplitudes. The spine can thus bend through greater amplitude than thatwhich is possible when the two spinous processes are secured to eachother in fixed manner.

FIG. 3 shows a second particular embodiment of the invention in whichthe wings of the notches, and the spinous processes which are insertedbetween them, are locked together by a pin which passes through thespinous processes.

FIG. 3 shows the intervertebral spacer between the two spinous processes34 and 36, and the pairs of wings 20, 21 and 22, 23 which engage partsof the processes 34 and 36. Furthermore, respective pins 40 pass throughthe notches 10′a and 12′a as well as through the spinous process 34 and36. The wings 20, 21 and 22, 23 are respectively pierced with two facingorifices through which the pins 40 can be inserted and fixed via theirends.

Prior to inserting the implant between the spinous processes 34, 36,said spinous processes are pierced laterally with respective orificeshaving a diameter that is greater than the diameter of the pins 40. Theintervertebral spacer is then inserted between the spinous processes 34,36, and the rivet-forming pins 40 are then slid through the wings 20, 21and 22, 23 and the corresponding spinous processes 34, 36. The ends ofthe pins 40 are flattened longitudinally in such a manner as to givethem a diameter that is greater than that of the orifices in the wings20, 21 and 22, 23 through which they pass. In this way, the pins 40 arelocked in longitudinal translation relative to the spacer, and the twoelements 10 and 12 are thus respectively secured to the spinousprocesses 34 and 36.

In this second particular embodiment of the invention, it is notnecessary to remove the interspinous ligaments or to disinsert thesupraspinous ligaments that underlie and overlie the intervertebralspace in which the spacer is to be inserted. During insertion of thespacer, since the pairs of wings 20, 21 and 22, 23 are notinterconnected by means suitable for surrounding the spinous process, itis necessary to remove the interspinous ligaments and to disinsert thesupraspinous ligaments only from the intervertebral space in which thespacer is to be inserted.

FIG. 4 shows a third embodiment of the invention providing the sameadvantages as those described above for the second embodiment.

FIG. 4 shows the intervertebral spacer between the two spinous processes34 and 36, and the pairs of wings 20, 21 and 22, 23 which engage partsof the processes 34 and 36. In contrast, the elements 10 and 12 of theintervertebral spacer are secured to the spinous processes 34 and 36 bymeans of respective clip-forming semicircular parts 42.

The semicircular part 42 includes two hook-forming ends that aredirected towards the inside of the part, and that are suitable for beinginserted into the orifices formed in the outside walls of the pairs ofwings 20, 21 and 22, 23. The part 42 is elastically deformable so thatit is force-fitted onto the elements 10 and 12.

Once the spacer has been inserted between the spinous processes 34, 36,the clips 40 are fixed on the elements 10 and 12 in such as manner thatthe inside walls of the semicircular parts 42 cover wall portions of thespinous processes that complement the wall portions of the spinousprocesses covered by the notches 10′a and 12′a. The spinous processes 34and 36 are thus held in the notches 10′a and 12′a by the clips 42,thereby securing the elements 10 and 12 to said spinous processes.

The above-described embodiments of the invention are not limited solelyto an intervertebral implant that is suitable for being interposedbetween two adjacent vertebrae. Thus, it is not beyond the ambit of theinvention to provide an implant that is constituted by two implants asdescribed above, which are interconnected via the ends of their wings,along their longitudinal axis, in such a manner as to limit and brakethe relative movements of three consecutive vertebrae.

1. An intervertebral implant designed to be applied between the spinousprocess of a first vertebra and the spinous process of a secondvertebra, the intervertebral implant comprising: a) a first elementhaving a base portion and first and second wings extending from the baseportion, the first and second wings of the first element defining afirst notch therebetween for placement of the spinous process of thefirst vertebra, wherein the first and second wings and the first notchof the first element are configured to extend around a portion of thespinous process of the first vertebra; b) a second element distinct fromthe first element, the second element having a base portion and firstand second wings extending from the base portion, the first and secondwings of the second element defining a second notch therebetween forplacement of the spinous process of the second vertebra, wherein thefirst and second wings and the second notch of the second element areconfigured to extend around a portion of the spinous process of thesecond vertebra; and c) a connection piece secured between the firstelement and the second element such that the first element and thesecond element are spaced from one another, the connection piece havinga first surface in direct contact with a first surface of the baseportion of the first element and a second surface in direct contact witha second surface of the base portion of the second element; the firstand second elements being formed of a first material and the connectionpiece being formed of a second material having an elastic deformabilitygreater than that of the first material, whereby the second material ofthe connection piece is compressible and elongatable to enable limitedrelative movement between the first and second vertebrae.
 2. Theintervertebral implant of claim 1, wherein the implant has a firstlateral side surface on a first side of the implant and a second lateralside surface on a second side of the implant; wherein the first elementextends from the first lateral side surface to the second lateral sidesurface, the second element extends from the first lateral side surfaceto the second lateral side surface, and the connection piece extendsfrom the first lateral side surface to the second lateral side surface.3. The intervertebral implant of claim 2, wherein the first lateral sidesurface extends along the first wing of the first element and the firstwing of the second element.
 4. The intervertebral implant of claim 3,wherein the second lateral side surface extends along the second wing ofthe first element and the second wing of the second element.
 5. Theintervertebral implant of claim 1, wherein the implant further comprisesa first pin passing laterally through the first and second wings of thefirst element configured to secure the spinous process of the firstvertebra in the first notch of the first element.
 6. The intervertebralimplant of claim 5, wherein the implant further comprises a second pinpassing laterally through the first and second wings of the secondelement configured to secure the spinous process of the second vertebrain the second notch of the second element.
 7. The intervertebral implantof claim 1, wherein the implant further comprises a first clipinterconnecting the first and second wings of the first elementconfigured to secure the spinous process of the first vertebra in thefirst notch of the first element.
 8. The intervertebral implant of claim7, wherein the implant further comprises a second clip interconnectingthe first and second wings of the second element configured to securethe spinous process of the second vertebra in the second notch of thesecond element.
 9. The intervertebral implant of claim 1, wherein theimplant further comprises a first tie having an adjustable lengthbetween the first and second wings of the first element configured tosurround a portion of the spinous process of the first vertebra tosecure the spinous process of the first vertebra in the first notch ofthe first element.
 10. The intervertebral implant of claim 9, whereinthe implant further comprises a second tie having an adjustable lengthbetween the first and second wings of the second element configured tosurround a portion of the spinous process of the second vertebra tosecure the spinous process of the second vertebra in the second notch ofthe second element.
 11. The intervertebral implant of claim 1, whereinthe second material adheres to the first material.
 12. Theintervertebral implant of claim 1, wherein the connection piece ismechanically secured to the first element and the second element. 13.The intervertebral implant of claim 1, wherein the first elementincludes a recess and the connection piece includes a projectionextending into the recess of the first element.
 14. The intervertebralimplant of claim 13, wherein the second element includes a recess andthe connection piece includes a projection extending into the recess ofthe second element.
 15. The intervertebral implant of claim 1, whereinthe connection piece is symmetrical about a central longitudinal axis ofthe implant extending through the first notch of the first element andthe second notch of the second element.
 16. The intervertebral implantof claim 15, wherein each of the first element and the second element issymmetrical about the central longitudinal axis.